Full Idea
Some statements predicate modality of another statement (modality 'de dicto'); but others predicate of an object the necessary or essential possession of a property; these latter express modality 'de re'.
Gist of Idea
Expressing modality about a statement is 'de dicto'; expressing it of property-possession is 'de re'
Source
Alvin Plantinga (De Re and De Dicto [1969], p.26)
Book Reference
Plantinga,Alvin: 'Essays in the Metaphysics of Modality' [OUP 2003], p.26
A Reaction
The distinction seems to originate in Aquinas, concerning whether God knows the future (or, how he knows the future). 'De dicto' is straightforward, but possibly the result of convention. 'De re' is controversial, and implies deep metaphysics.